As noted by A. Bannister and S. Raymond in Surveying, Pitman Publishing Ltd., London, 1977, general method of surveying was known and practiced more than 2000 years ago. The methods used at that time were simple but subject to consistency errors and required considerable time to perform. Surveying instruments have improved considerably since about 1900, taking advantage of advances in electronics, optics and other related disciplines. Recently, lasers, electro-optics, wave interaction and phase detection have been introduced into, and used in, surveying activities.
Use of a laser beam projector for surveying operations is disclosed in U.S. Pat. No. 3,471,234, issued to Studebaker. The beam rotates over terrain to be surveyed, and a beam point may be directed to a particular location and used to measure elevation and angular displacements within the region covered by the rotating beam.
Altman, in U.S. Pat. No. 3,669,548, discloses a method for determining a ship's heading or bearing, using an electro-optical angle measuring device that determines angles relative to a horizontal datum line. A plurality of parallel light beams, spaced apart by known, uniform distances and oriented at a known angle, forms a one-dimensional grid that covers the region where the ship is located. A rotating reflecting telescope on the ship has its axis aligned with one of the parallel light beams. The angle of the ship's longitudinal axis relative to the known direction of the parallel light beams is then easily read off to determine the ship's heading. This approach would not be suitable where the ship or other body whose angular orientation is to be determined can move over a large region.
Remote measurement of rotation angle of an object of interest by use of polarized light and electro-optical sensors is disclosed by Weiss et al in U.S. Pat. No. 3,877,816. The intensity of light transmitted serially through two linear polarization filters is proportional to the square of the cosine of the angle between the two polarization directions, and the proportionality constant can be determined by experiment. Unpolarized light transmitted along a first reference path with fixed polarization directions is compared with unpolarized light transmitted along a second, spatially separated and optically baffled path in which the polarization direction of one polarizer may vary. One or two light polarizers in each light beam path rotates at a constant angular velocity, which is the same for each path, and the difference in phase of the two received light signals is a measure of the angle of rotation of a polarizer (or the body to which the polarizer is attached) in the first path and a polarizer in the second path.
An optical-electronic surveying system that also determines and displays the angular orientation of a survey pole relative to a local horizontal plane is disclosed in U.S. Pat. No. 4,146,927, issued to Erickson et al. The system can receive and process range measurements directly from an electronic distance meter located near the system.
U.S. Pat. No. 4,443,103, issued to Erdmann et al, discloses use of a retro-reflective, electro-optical angle measuring system, to provide angle measurements after interruption of a signal that initially provided such information. A light beam is split into two beams, which intersect on a scanning mirror, which rotates or vibrates about a fixed axis, and the two beams are received at different locations on a retro-reflective tape positioned on a flat target surface on the target whose rotation is to be measured. These two beams form a plane that moves as the scanning mirror moves, with a reference plane being defined by the mirror at rest in a selected position. The scanning mirror sweeps the plane of the two beams across the target surface. A rotation angle of the target surface relative to the reference plane is determined, based upon the time difference between receipt of light from each of the two retro-reflected beams. The beam interception times coincide only if an edge of the retro-reflective tape is parallel to the reference plane. If receipt of light from the two retro-reflected beams is displayed on a synchronized, two-trace oscilloscope screen, the two "blips" corresponding to receipt of these two beams will have a visually distinguishable and measurable time difference .DELTA.t, as indicated in FIGS. 2A, 2B and 2C of the Erdmann et al patent. The time difference .DELTA.t will vary as the scanning mirror moves. A second Erdmann et al patent, U.S. Pat. No. 4,492,465, discloses a similar approach but with different claims.
"Total station" electronic instrumentation for surveying, and more particularly for measurement of elevation differences, is disclosed by Wells et al in U.S. Pat. No. 4,717,251. A rotatable wedge is positioned along a surveying transit line-of-sight, which is arranged to be parallel to a local horizontal plane. As the wedge is rotated, the line-of-sight is increasingly diverted until the line-of-sight passes through a target. The angular displacement is then determined by electro-optical encoder means, and the elevation difference is determined from the distance to the target and the angular displacement. This device can be used to align a line-of-sight from one survey transit with another survey transit or to a retro-reflector. However, the angular displacement is limited to a small angular sweep, such as 12.degree..
Fodale et al disclose an electro-optical spin measurement system for use in a scale model airplane wind tunnel in U.S. Pat. No. 4,932,777. Optical targets (six) to receive and sense one or several light beams are located under the fuselage at the nose tip, on each of two sides of the fuselage, and under each wing tip, and a plurality of optical receivers are positioned on the perimeter of the wind tunnel to receive light from the optical targets at various angles, to determine airplane angle of attack and roll angle. The time-synchronized signals received at each receiver are: recorded for subsequent analysis.
In U.S. Pat. No. 4,954,833, issued to Evans et al, information on deflection of the local vertical (obtained from gravity measurements) is combined with geodetic azimuth estimated from GPS signals to obtain an astronomical azimuth. This azimuth can be used for ballistic projectile delivery to a selected target. This method does not focus on integration of GPS operation with theodolite operation but, rather, seeks to avoid use of a theodolite to obtain the astronomical azimuth.
Kroupa et al, in U.S. Pat. No. 4,988,189, disclose use of a passive rangefinding system in combination with an electro-optical system, using image information obtained at two or more electro-optical system positions.
A method for simultaneously measuring the difference between orthometric (geoidal) height and height above a given ellipsoid for a site on the Earth's surface is disclosed by Evans in U.S. Pat. No. 5,030,957. Two or more leveling rods are held at fixed, spaced apart locations, with a known baseline vector between the rods. Each levelling rod holds a GPS signal antenna, receiver and processor that determines a GPS location for each rod. The geometric height of the GPS antenna (or of the intersection of the rod with the Earth's surface) is determined for each rod, and the geometric height difference is determined, using standard GPS survey measurements (accurate to within a few centimeters). A comparison of the orthometric height, usually found using a spirit level, and the height above the ellipsoid, obtained from a GPS measurement, provides a measure of the local gravitational field. The patent does not indicate, or perhaps recognize, advantages of use of height information to aid the GPS carrier phase initialization process but treats the GPS and the levelling rods as separate, non-interacting systems.
Ohishi et al disclose an optical distance measuring instrument using light transmitted and returned by retro-reflection in U.S. Pat. No. 5,054,911. A light beam pulse generated at the instrument is split into two pulses; one pulse is immediately received by a laser diode as a reference pulse. The other pulse is transmitted to a retro-reflector at a remote or adjacent target and returned to the instrument by retro-reflection thereat. The returning pulse is received by an optical fiber, having a known time delay .DELTA.t and then received by the laser diode to provide a second pulse. The time delay .DELTA.t is subtracted from the difference of arrival times of the two pulses and divided by 2c (c=ambient medium light velocity) to obtain the distance from instrument to target.
A somewhat unclear disclosure of a beam alignment apparatus and method is presented in U.S. Pat. No. 5,060,304, issued to Solinsky. Two substantially identical beam acquisition apparati are spaced apart from each other, each apparatus including two identical parabolic mirrors with parallel axes, each mirror having an axial aperture through which an electromagnetic wave beam passes and having a second smaller mirror located at the parabola's focal point. Each parabolic mirror has a third mirror consisting of a plurality of small retro-reflectors, located adjacent to but behind the parabolic mirror so that the parabolic mirror lies between the second and third mirrors. One parabolic mirror in each pair receives light from a transmitter positioned behind the mirror aperture and transmits this beam in a direction parallel to the mirror axis. The other parabolic mirror in each pair receives an incident beam propagating parallel to its axis and reflects this light to a receiver located behind the mirror aperture. One of the parabolic mirror pairs is operated in a search mode (moving) at a first selected frequency f1. The second parabolic mirror pair is operated in a "stare" mode at a selected frequency f2.noteq.f1. As the two mirror pairs come close to alignment with each other, the mirror pairs sense this by receipt of a retro-reflected beam or a directly transmitted beam, the distinction being made by the frequency of the beam received. The search mode mirror pair, and then the stare mode mirror pair, can then be brought into alignment with each other.
A surveying instrument that uses GPS measurements for determining location of a terrestrial site that is not necessarily within a line-of-sight of the surveyor is disclosed in U.S. Pat. No. 5,077,557 issued to Ingensand. The instrument uses a GPS signal antenna, receiver and processor, combined with a conventional electro-optical or ultrasonic range finder and a local magnetic field vector sensor, at the surveyor's location. The range finder is used to determine the distance to a selected mark that is provided with a signal reflector to return a signal issued by the range finder to the range finder. The magnetic field vector sensor is apparently used to help determine the surveyor's location and to determine the angle of inclination from the surveyor's location to the selected mark.
U.S. Pat. No. 5,101,356, issued to Timothy et al, discloses a moving vehicle attitude measuring system that mounts three GPS signal antennas in a non-collinear configuration on the vehicle at predetermined distances from each other. Each antenna is connected to a GPS receiver/processor. The phases of rf signals arriving at the antennas are compared to determine the angular orientation of the plane containing the three antennas, and the angular orientation of the vehicle that carries these antennas.
Method and apparatus for measuring the relative displacement of two objects, applicable to monitoring of movement of adjacent material along an earthquake fault, is disclosed in U.S. Pat. No. 5,112,130, issued to Isawa. First and second optical distance measuring instruments (ODMIs) are placed at known locations astride a selected line (e.g., a fault line). First and second optical reflectors, also astride the selected line, are spaced apart by known distances from the first and second ODMIs. Distances from the first ODMI to the second reflector and from the second ODMI to the first reflector are measured ab initio and compared with subsequent readings of these two distances. If one or both of these distances changes, the magnitudes of the changes are used to determine how far the Earth on one side of the line has moved relative to the Earth on the other side of the line, as might occur in a slip along a fault line.
Ghaem et al disclose an electronic direction finder that avoids reliance on sensing of terrestrial magnetic fields for establishing a preferred direction for satellite signal acquisition in U.S. Pat. No. 5,146,231. The apparatus uses a receiver/processor for GPS or similar navigation signals received from a satellite, and requires (stored) knowledge of the present location of at least one reference satellite from which signals are received. The orientation of the finder or its housing relative to a line of sight vector from the finder to this reference satellite is determined. This orientation is visually displayed as a projection on a horizontal plane. Any other direction in this horizontal plane can then be determined with reference to this projection from a knowledge of the reference satellite location.
U.S. Pat. No. 5,142,400, issued to Solinsky, discloses a method for line-of-sight acquisition of two optical beam transceivers suitable for use in satellite communications. A first beam transceiver has an optical retro-reflector and initially operates in a passive or "stare" mode, with its beam transmitted in a fixed direction. A second transceiver performs a search over 2.pi. steradians with its optical beam until it receives, from the first transceiver, either (1) a return of its own beam or (2) a distinguishable beam from the first transceiver. Boresight alignment is then maintained after beam-to-beam acquisition.
U.S. Pat. No. 5,146,290, issued to Hartrumpf, discloses apparatus for determining the position and angular orientation of an object. A partially silvered hemispherical light reflector is fixed to some part of the object, and two spaced apart laser beams are directed to intersect at the hemisphere center, to be (partly) retro-reflected at the hemisphere reflector surface, and to return toward the laser sources, to be detected by photodetectors located adjacent to each laser source. A portion of the beam from each laser source is transmitted through the hemispherical reflector and is received by a line or plane of photodetectors positioned on a plane behind the hemispherical reflector. As the object is translated or rotated, the locations where the reflected and transmitted beams are received by the photodetector arrays changes in a manner that can be related to the translation and/or rotation of the object.
A theodolite and tape have traditionally been used to measure horizontal and vertical angles and distances in terrestrial surveying. Recently, digital theodolites, as described in U.S. Pat. No. 3,768,911, issued to Erickson, and electronic distance meters (EDMs), as described by Hines et al in U.S. Pat. No. 3,778,159, have supplanted the theodolite and tape approach. Combination of an optical angle encoder and an EDM in an integrated package (called an "electronic total station"), as disclosed in U.S. Pat. No. 4,146,927, issued to Erickson et al, has led to automation of field procedures, plan production and design work.
Several limitations exist in use of a conventional total station. First, it is difficult to quickly establish the angular orientation and absolute location of a local survey or datum. Many surveys are not related to a uniform datum but exist only on a localized datum. In order to accurately orient a survey to a global reference, such as astronomical north, a star observation for azimuth is often used that requires long and complicated field procedures. Second, if a survey is to be connected to a national or state geodetic datum, the survey sometimes must be extended long distances, such as tens of kilometers, depending upon the proximity of the survey to geodetic control marks. Third, the electronic total station relies upon line-of-sight contact between the survey instrument and the rodman or pole carrier, which can be a problem in undulating terrains.
These systems do not provide the benefits of an integrated SATPS and terrestrial total station instrument. What is needed is a system that provides: (1) rapid azimuth and location determination in a fixed reference frame; (2) prompt resolution of the carrier phase ambiguities that occur in a SATPS; (3) distance and angle information without requiring line-of-sight contact between a reference station and a mobile station; (4) fail-safe capability for crosschecking, and calibrating the respective error sources in, the location information provided by the SATPS and by the terrestrial positioning system; and (5) capability for accounting for height differences between the geoid and ellipsoid over the local survey area.